Frequency generator with phase shifter



Jan. 19, T954 B. cARNlol. 2,666,851

,FREQUENCY GENERATOR WITHPl-IASE SHIFTER Filed Feb. 3. 1948 3 Sheets-Sheet 1 AMPLIHER- 9m j, 7

F Z AMPLIFIER fw y / f ==3 Amun;

9 a M fw @1@ Y Y#Ia-111.19, 1954 B. CARNIQL, 2,666,851

FREQUENCY GENERATOR WITH PHASE: SHIFTER Filed Feb. s, 1948 3 Sheets-Sheet 2 AMPLIFIER AMPLIFIER Jan. 19, 1954 B. cARNloL FREQUENCY GENER'ATOR WITH PHASE SHIFTER 3 Sheets-Sheet 3 Filed Feb. 5, 1948 A @5c/L A Taf .fm 65 AMPLIFIER 00 TFO T 67H66 Patented Jan. 19, 1954 UNITED STATES PATENT GFFICE FREQUENCY GENERATOR WITH PHASE SHIFTER Application February 3, 1948, Serial No. 5,973 In Czechoslovakia November 11, 1946 Section 1, Public Law 690, August 8, 1946 Patent expires November 11, 1966 (Cl. Z50- 36) 18 Claims.

This invention relates to comparison or compensation measurements of A. C. quantities and, more particularly, to an A. C. generator capable of producing a pair of voltages having a constant phase difference and a constant amplitude relationship irrespective of frequency.

Heretofore compensation methods have been used mainly for measuring direct voltages and currents. The use of compensation methods for measuring alternating voltages and currents is far less common than their use for measuring direct voltages and currents, due to the fact that compensation measurements in the alternating current field are considerably more difficult than in connection with direct currents. In the case of direct currents it is sufficient to effect amplitude compensation, while for alternating currents both amplitude compensation and phase compensation are necessary. In many cases it is required to effect measurements at different freof variable amplitude but also of variable phase and frequency is required.

In connection with the construction of generators and oscillators for alternating current compensators, three types of devices will be specifically referred to hereinafter:

(l) The so-called Franke-apparatus has two co-axial single phase generators of which one is provided with a movable stator to obtain two voltages with mutually measurable phase difference. The frequency may be varied by changing the angular velocity. This apparatus is used at present to a very limited extent due to its large size and to the impossibility of effecting measurements at high frequencies owing to the limited angular velocity.

(2) The low frequency oscillator whose output voltage is supplied to two output amplifiers, being led directly to one of the amplifiers and through a phase changer to the other. Then the desired frequency may be adjusted on the low frequency oscillator and the desired phase difference on the phase changer. The phase changer comprises ohmic and wattless components which may be varied to adjust the phase angle. In many cases a phasing element is used having a phase difference of 90. The desired phase angle may be easily adjusted by the aid of another phase changer, such as for instance a two-phase transformer, in which the primary is formed as the stator and the secondary as the rotor (booster).

or by means of a similar device (e. g. a circular potentiometer). Since the wattless impedances of the phase changer itself or of the phase element are dependent on the frequency, it follows that the calibration of the phase changer is valid only for a single frequency.

(3) The low frequency heterodyne oscillator, in which an acoustic frequency is obtained by mixing two high frequency oscillations having avariable frequency difference, i. e. one of the high frequency oscillators has a variable frequency.

If a phase shifter is inserted in the constantY frequency side of a high frequency oscillator, the phase of the resultant acoustic frequency is influenced without regard to the value of the frequency. Therefore the calibration of the phase shifter is valid for any desired low frequency. This arrangement eliminates the disadvantages appurtenant to compensators having phase shifters connected in the low frequency side of an oscillator. However, a new disadvantage arises due to the complexity of the apparatus and its limited frequency stability, particularly at the lowest frequencies. The low frequency of a heterodyne oscillator varies by the same value as in high frequency oscillators. Consequently, its relative frequency stability decreases, with a decrease in frequency, below that of high frequency oscillators. to the fourth or even higher order, the frequency stability is often insufficient.

The present invention eliminates the frequency instability and complexity of the foregoing arrangement by employing a low frequency oscil- In accordance with the present invention, anr oscillation generator is provided by an amplifier Y having its feed back coupling formed by a combination of frequency dependent impedances. This combination of frequency dependent impedances is selected to have such values that, throughout the frequency range it is possible to obtain two voltages having a constant amplitude ratio and q The voltages are V a constant phase shift of 90. utilised in a manner known per se to secure a continuous variation of phase by means,v for instance,

As this frequency difference amounts producing two A. C. voltages having a constant phase diierence and a constant amplitude relationship, irrespective of frequency, a common point of the two voltages being grounded.

Another object is the utilization of two sources of A. C. voltage of variable phase and constant` magnitude for compensation or comparison measurements of A. C. quantities over a wide range of frequencies.

A further object is to provide an R-C oscillation generator designed to produce two output voltages constantly in quadrature irrespective of frequency and having a; constant amplitude relationship equal to unity.

These, and other objects, advantages'and novel features of the invention willk be apparent from the following description and the accompanying drawings.

In the drawings:

Figs. 1- and 2- are block diagrams illustrating the principles of the R-C-oscillator of theY invention.

Figs. 3 through 6 are schematic wiring diagrams of various embodiments which the invenl tion may assume in practice.

Fig; '7l is a block diagram illustrating the invention. oscillator as incorporated in a comparison or compensation` measuring arrangement for A. C. quantities.

The circuit arrangements shown in Figs. l and 2 will` beA first described. I-nall gures of theY drawings an oscillator am-plier is denoted l. The feed back circuit of the latter is formedA by impedance elements-2; 3, 4,y 5. In accorda-ncewiththe present invention theunit comprising elements 2, 3 is connected inseries with the unit.

comprising elements ll, 5 and this series. connection.- of the two units as a whole isconnected to the output circuit of. the. amplifier I, while they unit4 2,4 3. which comprises a. resistance-anda capacity in series, is connected to. the input circuit: of the amplifier l. If.- the elementv 2 isa resistance,A the element 3, will be a capacity, While if theV element 2 isY a` capacity, the. element 3.

The-element 2 of this unit,

will be ar resistance. is always connected by means of one. of` its feed conductors to the ground connection Il of the amplier. In order that two alternating voltages having a constant amplitude ratio and shifted by 90 relative to each other independent of the frequency may be obtained from the oscillator and supplied to a phase shifter, the unit 2, 3, 4, 5, that is the output circuit of the amplifier I, is connected in parallel (Fig. 1), with a unit 6, comprising impedance elements such as resistances and capacities in different combinations which are shown by Way of example in Figs. 3, 4. and5. The element 1, which is either a capacityv or a resistance, is connected by means of one of its,y feed conductors to the ground connection ll of the amplifier' I. If the element 2 is a resistance, the element 'I will be a capacity and vice versa. The connection is made in such a Way that voltages e840 and eas, respectively, are impressed on the elements Zand l, which Voltages are shifted by 90 relative to each other and may be derived from the terminals l0 and 8 and the terminals 9 and 8, respectively.

In accordance with the invention, voltage in 90 phaserelation. may also. be. obtainedl by connecting in parallel to the amplifier input (Fig. 2) a unit 6, 1 consisting of impedance elements such as resistances and capacities so arranged that the element 1, which is either a resistance or a capacity, is connected by means of one of its feed conductors with the capacity or resistance 6, andy by meansV of its second feed conductor to the ground connection Il of the amplier l. In this way two voltages which may ce used for the, phase. shifter andare shifted by 90 relative to each other are again obtained between the pointsz 8, 9 andL I-.

Fig. 3 shows a typical circuit arrangement corresponding to the block diagram of Fig. l. In this example, the element 8 of the unit 'l connected in parallel to the amplifier output consistsv ofl a variable ohmic resistance R and the element' 'l` consists ofl a capacity. The element 2' consists of a variable ohm resistance and the ele,- ment 3 of a capacity. The resistances 2, d, 5

have the same value Rand the capacities 3, 5 T

have the same value C, as Well. With the use of thisV circuit arrangement, it will be demonstrated by calculation that the phasediflerence between the voltages 28,10 and 68,9 actually is 90 or of the voltage canl between points 8 to I Il toi the voltage 8,12 betweeny the points 8 andl |25. The ratio of the said. voltages is equal to` the ratio of the complexv resistances on which the said voltages arise. 'Therefore- 365.12.--4 Y Y K R+jw0 and this ratio is equalto, 1.5 for i Rc In order. to determine the phase difference between the voltages 68,9 and 98,10 we shall calculate first the phase difference of the said two voltages with respect to the total voltages. 8,14. The ratio 68.141 is again equal to the ratio of the complex resistances on which these voltages arise, orY for The equations II and III show that the voltages est and 8,10 are shifted relative to each other by or 90. This appears also from the equation for the ratio of these voltages or for the ratio ,d

of the Equations III and II.

This expression confirms the above aiirmation regarding the phase relation and shows moreover that the voltages 8,10 and est are in the ratio of 2 to 3. In accordance with the invention, the amplitude compensation may be eifected by connecting the member 6, 1 to the resistance i3 (R1) in the manner of a potentiometer.

By the same process of computing it may be proved that the circuit arrangement shown in Fig. 3 is equivalent to a circuit arrangement in which the element 2 is a capacity having the value C, the element 3 a resistance having the value R, the element l a resistance having the value R and the element 6 a capacity having the value C.

The frequency of the generator in the circuit arrangements shown in Fig. 3 may be varied either by simultaneous adjustment of the resistances R, as is shown in the drawing, or by simultaneous adjustment of the capacities. The variation may be either a continuous one, by providing for ganged potentiometers or condensers, or may be effected in steps by the use of a tapped switch. If it is desired to eiect the adjustment while avoiding variation of the total impedance and consequently of the load on the amplifier when a change in frequency takes place, a small resistance I3 (R1) is connected in parallel to the amplifier output. This resistance preferably is smaller than the resultant impedance of the units (2, 3, 4, 5) and (6, l) consisting oi resistances and capacities. In this way undesirable phase shift of the amplifier itself is avoided. If the frequency variation is effected by varying the capacities C of the condensers, the impedance of the whole arrangements is invariable as a function of the frequency.

Fig. 4 shows a further circuit arrangement corresponding to the block diagram of Fig. 1. In this example the elements of unit B, l are so chosen, that the element 1 is a capacity having a value 375C and the element 5 is a capacity which has a value 3C and is connected in series with a resistance having the value R. The element 2 is a resistance having the value R. With these values and the arrangement shown, the two voltages est and 68,10 have the same amplitude.

Fig. 5 shows a special circuit corresponding to the block diagram of Fig. l, wherein, in parallel with the amplifier output, there are connected four branches of a bridge which differ from cach other only in that in the units, each of which comprises a capacity connected in series with a resistance, the sequence of the elements is reversed.

Accordingly the element 'i is a capacity having the value C and the element 2 is a resistance having the value R. In view of the equivalency o1" the two circuit arrangements it is possible, of course, to use for the element 'l a resistance of the value R and for the element 2 a capacity of the value C. rfhe total impedance between the points S-ill is then resistive over the entire frequency range and the resistance R1 (I3) becomes superfluous.

Fig. 6 shows one circuit arrangement corresponding to the blocky diagram of Fig. 2. The unit 6, l is formed by tivo elements, a resistance and a capacity, the resistance 6 having a value 2R and the capacity a Value The unit 2, 3 comprises a resistance 2 of alvalue 2R and a capacity of a value The purpose of the arrangement is to obtain two voltages shifted in phase by 90 and at the same time to provide a unit which comprises-the elements 2, 3 and 8, l, and whose total resistance and capacity are equal to the resistance R and capacity C connected-up in series in the resistance-capacity unit. In all circuit arrangements shown in Figs. 4, 5 and 6 it is possible to prove by calculation that the voltages are actually phase shifted by 90, in the same manner as demonstrated for the arrangement shown in Fig. 3, and that the value of the voltage 88,9 is equal to the value of the voltage 63,10 for any desired requency.

Fig. '7 shows an example of the complete low frequency compensator. The block A comprises a low frequency R-C oscillator which, in accordance with the present invention, produces at 8-9 and S--i two equal voltages having a phase shift of 90, and a potentiometer for adjusting 4 and 6 simultaneously.

These voltages are fed to identical separating amplifiers II, III, which apply the voltages, at right angles to each other, to a circular potentiometer, or other suitable continuous phase adjusting device Pz. Block C contains two power ampliers IV, V, one for the constant direction voltage and the other for the phase adjusted voltage obtained from Pz. The frequency of both voltages is determined by adjustment of P1 in the oscillator stage A. The magnitude of the voltages is controlled by the potentiometers Ps,Y P4 in the output stage.

The arrangement of Fig. '7 thus provides a sim-- ple device, usable with an indicator of equal phasev scribed. For example, combinations of capaci-l tances and inductances, of resistances-and Vin-v accesar ductances, or of capacitances, resistances and in:- ductances may be used'. In practice, however, such combinations are notas desir-ablel as those specically exemplified due to instability of in the ground. The relative connections of' the feedback and. parallel circuits are reversed, to bring the series connected elements nearer to ground potential. In such case, the parallel con-. nectedY feedback resistance can` serve as a grid leak:

In, the block Bis arranged a circular potentiometer which is fed in two directionsl atright` angles to each other with two voltages from the generator over respective amplifiers. Beyond the block C two voltages may be branched oft', whose frequency may be controlled by a triple poten-v tiometer P1, the phase dilerence may be adjusted by a potentiometer P2 and the value may be adjusted by means of the potentiometers P3 and P4.

The present invention is not restricted to the circuit arrangements shown by way of example in the accompanying drawings. The invention relates in fact broadly to all circuit arrangements capable of supplying twealternating voltages of constant amplitude ratio and shifted in phase by 90 with, respect to each other, without being a function of fretpiency.v To secure a continuous,

variation of the phase, usev may be made of any of the known phase Shifters employing two voltages of the same amplitude and av phase difference of 90.

While specific embodiments of the invention have beeny shown and described in detail to illustrate the application of the principles thereto, itV l should be understood that the invention otherwise embodied without departing from such principles.

What I claimas my invention is:

1. In an oscillator circuit, an amplifier having a pair of inputfterminals and a pair of output terminals and zero phase shift, a common grounded. connection for one input and one out-- put terminal; a voltage -dividing feedback net` work connected between the output and the input of said amplier and comprising interconnected resistances and reactances; said network including a first section connected between the other output terminal and the otherinput terminal and comprising a resistance and a reactance inparallel circuit relation, and a second section connected between such other inputv terminal and said common connection and comprising a. resistance and a reactance in series circuit relation; a second voltage divider connected, be tween said, common connection and a point on said network and comprising interconnected re,-

sistances and reactances; means for applying a;

first alternating voltage between a point. on said' network and said common connection; and means for applying a second alternating voltagebetween a point on said second voltage divider and said common connection; said voltages having the same frequency, a constantly equa-l amplitude, and a quadrature phase relation;

2. An amplieras claimed in claim l in which said second voltage divider is connected in par,- allel with the--whole of said network.

3. An amplier as claimed in claim 1 in whichallel with the second section of said network.

4. An amplifier as claimed in claim. I including means operable to simultaneously vary the values of all the resistances of said network and second voltage divider.

5. An amplifier as claimed in claim 1 in which said reactan-ces comprise condensers, said second voltage divider is connected in parallel with the whole of said network, the relation of the series connected resistance and condenser ofsaid` second network section relative to said common connection being the reverseofz' that of the series connected resistance and condenser of said second divider, said points on said network and second voltagevdivider being the'junction of the'- series connected resistanceV and condenser, all ofV said resistances are equal in value and all of said reactances are equal in value.

6. An amplifier as claimed in claim 1 in which said reactances'comprise condensers, said second voltagev divider is connected in parallel with thewhole of said network; the relation ofthe series` connected resistance and condenser of said second network section relative to;said common connection being the reverse off that of the series connected resistance and condenser of said second divider, the reactance of said second divider comprising two series connected condensers having a magnitude ratio of' 1:2 with the smaller condenser being nearer said commonconnecti'on', said pointscn said network being thev junction of the series connected` resistance y andi condenser', said point on said' second dividerbeingfthejunc tion of the two condensers thereof', alli of" said resistances are equal. inY value, and the tota-l capacities of each combination being equal in value.

7. An amplifier as claimedlin' claim l` in' which said reactances comprise condensers, the second"A voltage divider comprises a parallel connectedresistance and'reactance combination and aiseries connected resistance and reactance combination in series with the parallel connected` combination, said second'voltage divider is connected in parallel withthe whole of saidnetwork, the rela tion ofr the series connected resistance and con-- denser of said second network section relativeto said' common connection being the reverse of' that of the series connected resistance and condenser'of saidv second divider, said points'` on said'. network being the `junction of' the series connected resistance and condenser, said point on said` second divider Ybeing the junction of" the, resistance and reactanceof theseries connected` combination, all of-I said resistances are equaliny value; and all ofsaidf reactances are' equalV in value.

8. An ampliiier'as claimedin claim 1 in which said reactancescomprisecondensers, said second; voltagel divider'is connected in parallel Iwith the second section off said network, the relation off the series connectedresistance and condenser oi` saidzsecond: networksection relative tojsaid' commonconnection being the reverse of thati of;l the..

series connected resistance andicondenser of said second, divider, said pointsonv said network. and second@ voltage dividerfbeing thei junction. of: the

series. connected resistance and-f condenser, andl the,s values-of the resistances: andi reactances of` the secondV network'section and. thez second volt`l age, dividerare one-half thevalue of. the, corre-- sponding` components ofthe. first networkV sec-- tion.

9; In'. an' oscillator circuit an ampliii'er having" a pair of inputV terminalsA andi a pair ofl output terminals; acommon connection for one input terminal and one output terminal; and a feedback network connected to the amplifier and including, a resistance-capacitance bridge comprising alternately arranged resistance and capacitance arms, the opposite resistance arms of said bridge being equal in value, a junction of said bridge being connected directly to said common connection and the opposite junction oi said bridge being connected directly to the other amplifier input terminal, and a parallel connected resistance-capacitance combination having one terminal connected to such opposite bridge junction and theA other terminal connected to the other amplier output terminal; and means for deriving a pair of constantly equal amplitude quadrature related voltages respectively between each of the other two junctions of said bridge and said common connection.

10. An oscillator circuit as claimed in claim 9 in which all said resistances have the same value.

11. An oscillator circuit as claimed in claim 9 in which all said capacitances have the same value.

l2. An oscillator circuit as claimed in claim 9 in which all said resistances have the same value and all said capacitances have the same value.

13. An oscillator circuit as claimed in claim 9 in which the bridge resistances have twice the value of the combination resistance and the bridge capacitances have one-half the value of the compensation capacitance.

14. In an oscillator circuit, an amplier having a pair of input terminals and a pair of output terminals; a common connection for one input terminal and one output terminal; and a feedback network connected to said amplier and including a resistance-capacitance bridge comprising alternately arranged resistance and capacitance arms, the opposite resistance arms of said bridge being equal in value, a junction of said bridge being connected directly to said common connection and the opposite junction of said bridge being connected to the other ampliiier input terminal, and a parallel connected resistance-capacitance combination; a connection between one terminal of said combination and the other amplifier output terminal; a connection between the other terminal of said combination and the other ampliiier input terminal; and means for deriving a pair of i constantly equal amplitude quadrature related voltages respectively between each of the other two junctions of said bridge and said common connection.

15. In an oscillator circuit, an amplifier having a pair of input terminals and a pair of output terminals; a common connection for one input terminal and one output terminal; and a feedback network connected to said amplier and including a resistance-capacitance bridge comprising alternately arranged resistance and capacitance arms, the opposite resistance arms of Said bridge being equal in value, a junction of said bridge being connected directly,T to said common connection and the opposite junction of said bridge being connected to the other amplifier input terminal and a parallel connected resistance-capacitance combination; a connection between one terminal of said combination and the other amplifier output terminal; a connection between the other terminal of said combination and the other amplifier input terminal; means for deriving a pair of constantly equal amplitude quadrature related voltages respectively between each of the other two junctions of said bridge and said common connection; and an additional capacitance in series with a resistance arm of said bridge; said resistances all having the same value, the additional capacity having three times the value of the combination capacity, the capacity in the adjacent bridge arm having 1.5 times the value of the combination capacity, and the other bridge capacity being equal in value to the combination capacity.

16. In an oscillator circuit, an amplilier having a pair of input terminals and a pair of output terminals; a common connection for one input terminal and one output terminal; and a feedback network connected to said amplifier and including a resistance-capacitance bridge comprising alternately arranged resistance and capacitance arms, the opposite resistance arms of said bridge being equal in value, a junction of said bridge being connected directly to said common connection and the opposite junction of said bridge being connected to the other amplifier input terminal, and a parallel connected resistance-capacitance combination; a connection between one terminal of said combination and the other amplifier output terminal; a connection between the other terminal of said combination and the other amplier input terminal; means for deriving a pair of constantly equal amplitude quadrature related voltages respectively between each of the other two junctions of said bridge and said common connection; and e second parallel connected resistance-capacity combination, equal in R and C values to the rst combination, connected in series with another arm of said bridge.

17. In an oscillator circuit, an amplifier having a pair of input terminals and a pair of output terminals; a common connection for one input terminal and one output terminal; and a feedback network connected to said amplifier and including a resistance-capacitance bridge comprising alternately arranged resistance and capacitance arms, the opposite resistance arms of said bridge being equal in value, a junction of said bridge being connected directly to said common connection and the opposite junction of said bridge being connected to the other amplifier input terminal, and a parallel connected resistancecapacitance combination; a connection between one terminal of said combination and the other amplifier output terminal; a connection between the other terminal of said combination and the other amplier input terminal; means for deriving a pair of constantly equal amplitude quadrature related voltages respectively between each of the other two junctions of said bridge and said common connection; and a second parallel connected resistance-capacity combination, equal in R and C value to the irst combination, connected in series with a resistance arm of said bridge.

i8. In an oscillator circuit, an amplifier having a pair of input terminals and a pair of output terminals; a common connection for one input t rminal and one output terminal; and a feedback network connected to said amplifier and including a resistance-capacitance bridge comprising alternately arranged resistance and capacitance arms, the opposite resistance arms of said bridge being equal in value, a junction of said bridge being connected directly to said common connection and the opposite junction of said bridge being connected to the other amplifier input terminal, and a parallel connected resistance-capacitance combination; a connection :between one terminal of said combination and the other amplier Youtput terminal; a ,connection between the other terminal of said vcombination and the other amplier input terminal; and means for deriving a pair of constantly equal amplitude quadrature related voltages respec- ,tively between each of the other two junctionsof vsaid bridge and said .common connection; Vall of said resistances being variable and gauged for simultaneous variation.

vBOHDAN CARNIOL.

Number Name Date Lyle Feb. 11, 1936 Plebanski Nov. 1, 1938 Wintringham Feb. 21, 1939 Hewlett Jan. 6, 1942 Dunn Apr. 6, 1948 Gassel et al. Aug. 10, 1948 Mork Oct. 19, 1948 Osterlund et a1. Aug. 1, 1950 

